This invention relates to electron beam systems such as scanning and non-scanning electron microscopes, electron beam lithography systems, and the like.
One class of such systems utilizes a thermionic source. Another smaller class of high performance systems utilizes a high brightness electron source such as a field emission cathode. The cost of such high performance systems is in general very much greater than that of the class of systems using thermionic sources due in large part to the very high cost of the ultra high vacuum equipment needed to pump such systems to the ultra high vacuum levels which are needed to support the field emission source--typically 10.sup.-9 to 10.sup.-10 torr.
There is a strong need for a system having the high performance of systems having field emission sources but with a cost more comparable to that of systems with thermionic sources.
It is an object of this invention to provide an electron beam system having a high brightness electron beam source not requiring a costly high vacuum pumping system, and thus an electron beam system with the desirable capabilities attending use of a high brightness source at a cost more typical of systems having much less capable sources.
It is an object to provide an electron beam system which has a self-pumped high brightness source, such as a field emitter, and which is much less expensive to manufacture than conventional high brightness source systems.
It is an object of this invention to provide an encapsulated high brightness source for electron beam systems which may be modular in construction. More specifically, it is an object to provide a modular encapsulated high brightness source which can be installed as original equipment or as a retrofit in various electron beam systems of the types adapted for a thermionic source, lending the high performance associated with high brightness sources to systems of the type normally employing a thermionic source.
It is an object to provide such a modular encapsulated source which is capable of being assembled, tested and stored in an operative condition for quick and easy installation as original equipment in an electron beam system, or as a replacement part or retrofit.
It is yet another object to provide such a modular encapsulated high performance source which is relatively low in manufacturing cost.
It is still another object to provide an encapsulated source, modular or built-in, which is readily adapted for low voltage applications wherein it is desired to have low electron beam energy, as where electron charge-up is undesired, or wherein the specimen is fragile.
It is an object to provide such a source which can be adapted for attachment to or incorporation in the high voltage terminal of any microscope having typical moderate or high operating voltages--for example, in the range of 50 Kv to 1 million volts.
It is yet another object to provide such a source which is capable of preserving its ultra high vacuum state even in the event of sudden loss of vacuum in the associated electron beam system.
It is still another object to provide such a source which has a long shelf life and a long operating life.
It is a further another object of this invention to provide such a source offering convenient adjustment of operating beam voltage and current, and precise control of the location of the effective electron point source.